The 2.23 kb gene encoding the fimbrial-associated adhesin of P.loescheii PK1295 has been cloned and sequenced. The gene contains a ribosomal slip which results in a reading frame shift and a failure to translate the 28 bases found prior to the shift. Attempts to express the gene in a number of E.coli host strains have met with limited success. Clones containing vector-gene constructs appear to be near lethal; in the two instances where expression was observed both plasmid vector and gene were quickly lost. Presently, new strategies are being tested to stabilize constructs. The receptor for the Actinomyces israelii- specific fimbrial adhesin of P. loescheii has been extracted from the cells of A. israelii PK14 and purified by column chromatography. Preliminary results indicate that it contains neither protein nor carbohydrate reducing sugar, but the material does contain phosphorus. The purified material is capable of aggregating P. loescheii and certain Streptococcus sanguis cells. The gene encoding the xylitol and ribitol pathway enzymes are currently being cloned. A 6.2 kb chromosomal DNA fragment containing the entire ribitol-5-P dehydrogenase (RDH) gene has been ligated into pBluescript II SK and transformed into an E. coli host. Expression of the gene product was detected with anti-RDH IgG on immunoblots and active dehydrogenase was detected in cell extracts containing the cloned DNA. DNA fragments containing the xylitol-specific Factor III and xylitol-5-P dehydrogenase are currently being ligated into pBluescript II also.